It is known as from Davies U.S. Pat. No. 2,753,831 to provide an air filter clogging warning apparatus in which a whistle is secured within a tube which extends through the filter, the tube being affixed in the filter by a funnel shaped portion at its upstream end and a washer affixed adjacent its downstream end. Said patent also contemplates the provision of a screen over the mouth of the funnel shaped end of the tube.
It is also known to provide whistles and vibrating reed warning devices in connection with carburetor air intake filters to signal when the filters are clogged and in need of replacement as exemplified by the following U.S. Pat. Nos.: Wickersham 1,770,094; Smith 1,863,456; and Nowicki 3,529,407; 3,699,749; 3,737,900; and 3,740,931.